Recently, ceramic materials have found increasing use in various technical fields. In view of the temperature resistancy and form consistency they may be used under conditions where organic synthetics fail. Nevertheless, there is still a problem with using ceramic materials for manufacturing elements specifically of complex form, e. g. hollow bodies. Up to now mass production is possible for ceramic parts of very simple shape which may be formed in green state by usual pressing tools, for example, in dry pressing processes followed by a burning or sintering step. Ceramic hollow bodies have been produced by the so called ooze or slime molding method where a watered ceramic powder is condensed in a closed mold having porous walls by removal of liquid through these walls. However, the density achieved and, therefore, the stability of such bodies are unsatisfactory depart from the method being cumbersome and energy consuming, thus applicable only for a piece-by-piece production.
Alternatively, ceramic bodies of complex shape, specifically provided with cavities may be produced by the so called laminating technique (U.S. Pat. Nos. 4,864,271; 4,972,579; 4,894,635). Here, a plurality of thin green ceramic foils having desired outer contoures or inner openings are formed to a stack followed by burning or sintering of the so formed body. Inner spaces have to be filled with corresponding rigid inserts which are evaporated or sublimated during the burning step. It is clear that such a laminating technique is difficult to process specifically when manufacturing relatively small elements.
The U.S. Pat. No. 4,481,497 discloses a pressure sensor employing a ceramic substrate and a ceramic diaphragm formed as separate parts and connected together. The substrate is provided with a cavity allowing deformation of the diaphragm. The diaphragm is provided with transducer means comprising a resistor bridge. Again, the known pressure sensor is complex in design and costly to be manufactured.
The DE-A-35 10 042 (U.S. Ser. No. 591,728) discloses a pressure sensor comprising a pressure transducer and a pressure measuring capsule. The capsule includes a membrane in surface contact with a diaphragm of the pressure transducer. The membrane of the capsule forms one wall of a cavity further defined by an opposite rigid plate and flexible transition portions connecting this plate with the membrane. Again, the design of the known pressure transducer is complex and the manufacturing thereof costly.
The U.S. patent application Ser. No. 322,142 relates to a pressure transducer comprising a rigid body formed of ceramic material with a ring-like shape having a central opening and a radially extending plane end surface, a diaphragm unitary with the rigid body and covering the opening at an end surface opposite to the plane end surface and thickfilm resistor means applied to at least one of two main surfaces of the diaphragm. Whilst this pressure transducer has a relatively simple design and is easy to be manufactured, it is difficult to position and fix it to a measuring position with the tendency of the diaphragm to be inadvertently tensioned or twisted.
The European patent application 0 232 048 discloses a ceramic arc tube for a high-pressure metal-vapor discharge lamp which is produced by forming a green ceramic tubular body of a first ceramic material; forming at least one green end cap of a second ceramic material the end cap including a cylindrical portion and a flange portion; positioning the cylindrical portion into a corresponding end portion of the green ceramic tubular body and burning the assembly. The ceramic material for the green ceramic tubular body may have a greater burning shrinkage than the ceramic material for said end cap. There is neither a diaphragm provided nor a connecting joint for connection to a fluid path.
The European patent No. 0 142 852 discloses a method of connecting of two halves of a hollow body made of green ceramic. Specifically, a semisphere body portion is inserted into one of two pressing molds each. By moving the pressing molds toward each other contact surfaces of the two halves engage each other. Integration at the contact surfaces is achieved by applying vibrations to one of the pressing molds. Then, the completed sphere is burned. There are no diaphragm and connecting joint formed to the sphere. Furthermore, the method is not adapted for mass production since each sphere must be individually formed under vibration.
There is another problem with the use of ceramic bodies: It is relatively difficult to fix them at a desired device of use. Up to now complex metallic clamping devices or housings are necessary or a metallic connecting element is embedded into the ceramic body by very specific technical processes.
U.S. Pat. No. 4,894,635 discloses a typical example for mounting a strain sensor formed of ceramic material by the above mentioned laminating technique. Specifically, the ceramic body is accommodated within a housing which is covered by a lid member. The three members are maintained in the assembled state by a cauling member engaging the housing body and the lid member pressing the peripheral part of the ceramic body against the housing body. An O-ring is interposed between the lower surface of the ceramic body and the opposite inner surface of the housing body. The housing body has a pressure hole formed therethrough communicating with a through-passage in the ceramic body. The housing body has formed thereon a stub provided with an outer threading for connection to a path means. It will be appreciated that this is a rather complex mounting means for the ceramic body.
Similarly, U.S. Pat. No. 4,898,035 discloses a pressure sensor including a cylindrical metallic housing having an open end portion in which the ceramic sensor is fixedly accommodated. A metallic sealing member in the form of an annular disk having an opening is fluid-tightly secured at its radially inner portion to the radially outer or peripheral portion of the bottom wall of the ceramic body via an annular bonding layer formed of a glass or brazing material. This assembly is accommodated in a fluid-tight manner into a cylindrical metallic housing.
Furthermore, U.S. Pat. No. 4,934,193 discloses a pressure sensing transmitter comprising a housing. The housing is made of stainless steel and a metal isolation diaphragm is joined to the housing. An isolation fluid is sealed in a space between said isolation diaphragm and the sensing surface of the ceramic sensor. The metallic housing is provided with a passage having an inner threading for connection to a fluid path.